Dating the topography through thermochronology: application of Pecube code to inverted vertical profile in the eastern Sila Massif, southern Italy

Volume:136 (2017) f.3 Pages:321-336 DOI:10.3301/IJG.2016.09

Abstract

AbstractThe Sila Massif is a small part of an orogenic wedge that sits on top of the narrow and active Calabrian subduction zone. The topography of the Sila Massif is characterized by a plateau region whose age and origin has been long debated. Here we integrate new apatite (U-Th)/He data from the eastern flank of the massif with existing apatite fission-track (AFT) data, to constrain the topographic evolution of the massif. The new AHe ages range from 9.7 Ma to 49.8 Ma and overlap the AFT ages indicating that a phase of rapid Cenozoic exhumation was followed by an abrupt decrease of the exhumation rate. A steep/inverse AFT age-elevation relationship from a vertical profile on top of the summit area of the north-eastern Sila may records post-exhumation relief degradation, which is consistent with the low-relief upland topography. To test this hypothesis we performed inverse numerical modeling using Pecube code. Integrating the new AHe ages and the numerical modelling results with the geological constraints we propose a new model for the regional topographic evolution from 30 Ma to the present.

AbstractThe Strait of Messina area has been affected by strong uplift, which caused the development of spectacular sequences of Pleistocene coastal marine terraces. A new detailed mapping of the terraced surfaces has been carried out on both sides of the northern sector of the Strait. In the Calabrian side, a complete sequence of ten fluvial-coastal terraces has been recognized at elevations ranging from 40 to 520 m a.s.l. and dated from 60 to 330 ka. The series is partly displaced by normal faults bordering the structural high of Campo Piale and the estimated uplift rates change in time and space in response to the fault activity. They range from 1.5 mm/yr for the period 330-200 ka, on the Campo Piale high, to 0.8 mm/yr for the period 125-60 ka, on the hanging wall of the Scilla Fault that borders the Campo Piale high to the north. The constant elevation of the I order terrace suggests an uniform uplift rate of 1.4 mm/yr along the Villa San Giovanni coastal area and the termination of the western sector of the Scilla Fault, even though the offshore activity of segments belonging to the same system is not excluded. In the Sicilian side, six orders of terraces have been recognized on the Capo Peloro promontory. Their inner edges range in elevation from 30 m to 170 m a.s.l., the age attribution varies from 60 to 240 ka. The series is tilted of ~10-15° southward due to the activity of the Mortelle Fault, bounding the promontory to north. The elevation of inner edges suggests that the uplift process, characterized by rate of 0.8 mm/yr, has undergone an acceleration during the late Pleistocene, probably related to activity of offshore structures.

Styles and rates of deformation in the frontal accretionary wedge of the Calabrian Arc (Ionian Sea): controls exerted by the structure of the lower African plate

Volume:136 (2017) f.3 Pages:347-364 DOI:10.3301/IJG.2016.11

Abstract

AbstractThe Calabrian Arc is a narrow subduction-rollback system resulting from Africa/Eurasia plate convergence. We analysed the structural style of the frontal accretionary wedge through a multi-scale geophysical approach. Pre-stack depth-migrated crustal-scale seismic profiles unravelled the overall geometry of the subduction complex; high-resolution multi-channel seismic and sub-bottom CHIRP profiles, together with morpho-structural maps, integrated deep data and constrained the fine structure of the frontal accretionary wedge, as well as deformation processes along the outer deformation front.
We identified four main morpho-structural domains in the western lobe of the frontal wedge: the proto-deformation area at the transition with the abyssal plain; two regions of gentle and tight folding; a hummocky morphology domain with deep depressions and intervening structural highs; a highstanding plateau at the landward limit of the salt-bearing accretionary wedge, where the detachment cuts through deeper levels down to the basement. Variation of structural style and seafloor morphology in these domains are related to a progressively more intense deformation towards the inner wedge, while abrupt changes are linked to inherited structures in the lower African plate. Our data suggest focusing of intense shallow deformation in correspondence of deeply rooted faults and basement highs of the incoming plate.
Back-arc extension in the Southern Tyrrhenian Sea has recently ceased, producing a slowdown of slab rollback and plate-boundary re-organization along trans-tensional lithospheric faults segmenting the continental margin. In this complex setting, it is not clear if the accretionary wedge is still growing through frontal accretion. Our data suggest that shortening is still active at the toe of the wedge, and uplift rates along single folds are in the range of 0.25-1.5 mm/yr. An unconformity within the Plio-Quaternary sediments suggests a discontinuity in sedimentation and tectonic processes, i.e. a slowdown of shortening rate or an increase in sedimentation rate, but not a real inactivation of frontal accretion, which still contributes to the migration of the outer deformation front towards the foreland.

AbstractFor any scientist working in seismotectonics, the Calabrian Arc represents the most challenging area of Italy. Lying on top of a subduction zone, it is characterised by a complex geological structure largely inherited from the early stages of the collision between the Africa and Eurasia plates. The current and extremely vigorous seismogenic processes, although generated by a mechanism driven by the subduction, are no longer a direct consequence of plate convergence.
About one fourth of the largest Italian earthquakes concentrates in a narrow strip of land (roughly 200x70 km) corresponding to the administrative region of Calabria. The present-day seismicity, both shallow and deep, provides little help in detecting the most insidious seismogenic structures, nor does the available record of GPS-detected strains.
In addition to its fierce seismicity, the Calabrian Arc also experiences uplift at rates that are the largest in Italy, thus suggesting that active tectonic processes are faster here than elsewhere in the country.
Calabrian earthquakes are strong yet inherently elusive, and even the largest of those that have occurred over the past two centuries do not appear to have caused unambiguous surface faulting. The identified active structures are not sufficient to explain in full the historical seismicity record, suggesting that some of the main seismogenic sources still lie unidentified, for instance in the offshore. As a result, the seismogenic processes of Calabria have been the object of a lively debate at least over the past three decades.
In this work we propose to use the current geodynamic framework of the Calabrian Arc as a guidance to resolve the ambiguities that concern the identification of the presumed known seismogenic sources, and to identify those as yet totally unknown. Our proposed scheme is consistent with the location of the largest earthquakes, the recent evolution of the regions affected by seismogenic faulting, and the predictions of current evolutionary models of the crust overlying a W-dipping subduction zone.

Seismotomographic detection of major structural discontinuity in northern Sicily

Volume:136 (2017) f.3 Pages:389-398 DOI:10.3301/IJG.2016.14

Abstract

AbstractWe present the results of tomographic inversion computed with the use of the LOTOS code for Sicily and surroundings, a region of great geodynamic interest located on the Nubia-Europe margin where previous analyses have progressively improved the knowledge of seismic velocity structure without, however, permitting fine detection of tectonic units and structural discontinuities. We used LOTOS's devices for inversion, grid rotation and adaptation to ray density for application to a dataset of 7105 local earthquakes of the period 1990-2012. Our tomographic model highlights a previously undocumented major discontinuity which is located approximately along the northern coast of Sicily and is characterized by a sudden transition from low velocity imbricate thrust sheets and accretionary wedge in mainland Sicily (to the south) to relatively high velocity Tyrrhenian continental crust (to the north). Combining this finding with available geological and geodynamic information, we conclude that this northern Sicily seismic velocity discontinuity, which approximately corresponds to a regional fault system known as Kumeta-Alcantara, may have played a major role in the Miocene to Middle Pliocene, when lithosphere tearing occurred between the Tyrrhenian sea and Sicily in response to trench retreat. The more recent geodynamic settings of northern Sicily and the southern Tyrrhenian can be unravelled from Quaternary geological observations, seismicity and GPS data, which indicate that (i) the northern Sicily discontinuity has ceased to be active in more recent times; and (ii) the reorganized slow convergence of Nubia with respect to Europe is currently accommodated ~100 km north of Sicily, along the east-trending seismogenic belt enclosing Ustica and the Aeolian Islands.

Structural architecture and active deformation pattern in the northern sector of the Aeolian-Tindari-Letojanni fault system (SE Tyrrhenian Sea-NE Sicily) from integrated analysis of field, marine geophysical, seismological and geodetic data

Volume:136 (2017) f.3 Pages:399-417 DOI:10.3301/IJG.2016.17

Abstract

AbstractFramed in the current geodynamics of the central Mediterranean, the Aeolian-Tindari-Letojanni fault system is part of a wider NW-SE oriented right-lateral wrench zone which accommodates diverging motion between regional-scale blocks located at the southern edge of the Calabrian Arc. In order to investigate the structural architecture and the active deformation pattern of the northern sector of this tectonic feature, structural observations on-land, high and very-high resolution seismic reflection profiles, swath bathymetry and seismological and geodetic data were merged from the Lipari-Vulcano volcanic complex (central sector of the Aeolian Islands) to the Peloritani Mountains across the Gulf of Patti. Our interpretation shows that the active deformation pattern of the study area is currently expressed by NW-SE trending, right-transtensional én-echelon fault segments whose overlapping gives rise to releasing stepover and pull-apart structures. This structural architecture has favored magma and fluid ascent and the shaping of the Lipari-Vulcano volcanic complex. Similarly, the Gulf of Patti is interpreted as an extensional relay zone between two overlapping, right-lateral NW-SE trending master faults. The structural configuration we reconstruct is also supported by seismological and geodetic data which are consistent with kinematics of the mapped faults. Notably, most of the low-magnitude instrumental seismicity occurs within the relay zones, whilst the largest historical earthquakes (1786, Mw=6.2; 1978, Mw=6.1) are located along the major fault segments.

Present-day kinematics and deformation processes in the southern Tyrrhenian region: new insights on the northern Sicily extensional belt

Volume:136 (2017) f.3 Pages:418-433 DOI:10.3301/IJG.2017.01

Abstract

AbstractWe performed a new analysis of updated and accurate sets of seismic and GNSS data relative to the southern Tyrrhenian region. Detailed velocity field and crustal strain distribution coming from integration of episodic and continuous measurements at more than 160 geodetic sites (spanning the 1994-2015 period) have been evaluated together with the spatial distribution of recent seismicity and an updated catalogue of waveform inversion fault-plane solutions relative to the period 1976-2014. In agreement with previous investigations, we have found that the kinematics of the study area is quite homogeneous except for the north-eastern corner of Sicily which moves almost coherently with southern Calabria in response to the SE-ward rollback of the Ionian slab. The rest of the study region shows a NNW-trending velocity field in agreement with the direction of the Nubia-Eurasia convergence and it is mainly interested by a major compressive domain. NNW-oriented compression is particularly highlighted by seismic data along the E-W trending seismic belt located in the southern Tyrrhenian Sea. In the framework of such compressive regime, the E-W trending extensional domain of northern Sicily is also clearly depicted both by seismic and geodetic data. The cause of this extensional domain framed inside a mainly compressive one represents an open question in the recent scientific debate. Comparisons between our results and literature information on regional geology and crustal structure led us to investigate whether the extension could occur as local response to the thrusting dynamics of the southern Tyrrhenian belt, favoured by the presence of pre-existing weakness zones. We then propose a first attempt to evaluate such a possible causal relationship by means of Finite Element Method (FEM) and Coulomb Stress Change (CSC) modelling. In particular, we adopted a FEM approach to investigate the deformation pattern produced by thrust faulting of southern Tyrrhenian belt, along a 2D profile crossing both the compressive belt and the extensional one in northern Sicily. We also estimated the CSC due to the thrust faulting on normal receiving faults fairly reproducing pre-existing structures of northern Sicily. Modelling results indicate that the thrust faulting activity along the Southern Tyrrhenian compressive margin could be effective in promoting extensional processes in northern Sicily. We have so shown that the local response to thrust faulting activity may concur, even in combination with other processes, to generate the crustal stretching of northern Sicily.

Structural style of Quaternary extension in the Crati Valley (Calabrian Arc): Evidence in support of an east-dipping detachment fault

Volume:136 (2017) f.3 Pages:434-453 DOI:10.3301/IJG.2017.11

Abstract

AbstractNew geological field data, integrated with commercial seismic lines, allowed us to constrain the geometry and time-space evolution of the fault system that ruled the tectono-sedimentary evolution of the NS-striking Crati graben, in the axial portion of the northern Calabrian Arc.
We highlight that this basin is controlled by a 60-km long east-dipping master fault, referred to as the Crati Graben Detachment Fault (CGDF).
On the seismic sections, the CGDF appears as an east-dipping low-angle reflection reaching the surface along the eastern slope of the Catena Costiera Calabra. Its surface expression corresponds to an alignment of moderately-inclined (30° to 45°) left-stepping en-échelon faults.
More to the East, a number of E- and W-dipping high-angle normal faults branch upward from the CGDF. Their reconstructed timing suggest that the westernmost faults are active since the Early Pleistocene and show a progressive eastward rejuvenation trend.
The conversion to depth of a W-E oriented seismic section, crossing the entire Crati graben, highlights that the CGDF has a staircase geometry, with an average angle of 30°, and reaches a depth of 7-8 km below the east side of the basin. The evolutionary stages of the related fault system were reconstructed by restoring the section through the Move suite software (Midland Valley Exploration), in order to verify the kinematic consistency of our subsurface interpretation and estimate the amount of associate extension.
Finally, the present activity and the possible seismogenic role of the CGDF is preliminarily discussed, by comparing the geometry of the extensional fault system with the available historical and seismological instrumental datasets.

Uplifted Late Holocene shorelines along the coasts of the Calabrian Arc: geodynamic and seismotectonic implications

Volume:136 (2017) f.3 Pages:454-470 DOI:10.3301/IJG.2017.13

Abstract

AbstractLate Holocene (~6.5 ka) shorelines represented by tidal notches, beach deposits, wave-cut terraces and intertidal organic rims are raised from few decimetres up to 5.5 m above the present sea level in the southern part of the Calabrian Arc, southern Italy. At five localities (Capo Vaticano and Scilla in southern Calabria and Taormina, Schisò, Capo Milazzo in north-eastern Sicily), the uplifted paleo-shorelines form a distinct vertical sequence where the older shorelines rest invariably above the younger ones. Such arrangement documents the occurrence of abrupt uplift events that, within the limits imposed by existing age controls, we attribute to ancient earthquakes. A comprehensive appraisal of published studies has allowed to draw an inventory with a total of possibly sixteen earthquakes which, based on the amount of shoreline displacement (~0.5-2 m) and the length of coastal section involved in uplift, were likely to be of strong size. It appears that the amount of uplift decreased with time during the Late Holocene at all sites but Capo Vaticano, where it remained almost stationary. The co-seismic events appear grouped within four temporal clusters, during which uplift occurred at most of the five coastal sectors investigated here. These clusters spanned time intervals whose duration, although difficult to bracket with precision, is of few hundred years, and are separated by longer (~0.5-1.5 ka) periods of apparent tectonic quiescence. The sources of co-seismic uplifts are still undefined, and should be searched between normal faults in the stretched Calabrian upper crust, or lower crustal thrust faults related to the Ionian subduction.

1876-1881: Domenico Lovisato and the geology of Calabria (Southern Italy)

Volume:136 (2017) f.3 Pages:471-484 DOI:10.3301/IJG.2017.10

Abstract

AbstractCelebrating the centennial of Domenico Lovisato's death (1842- 1916), this paper highlights the role played by this eminent Italian geologist as a pioneer for the geological knowledge of Calabria region (Southern Italy), a geologically complex area which became the subject of a long-lasting and still continuing debate.
Lovisato spent only few years in Calabria (1876-1878) teaching as high school professor of mathematics; this period marked a turning point for his scientific growth representing a switch for his career from avocational to full-time geologist. This experience granted him the involvement in the academic career, with the enrollment in the niversity of Sassari and Cagliari as Professor of Mineralogy and Geology (from 1878 until his death, in 1916). Lovisato must be acknowledged as the author of the first 1:50,000 geological map of the Calabria region. As such, he should be mentioned for his ethic approach towards environment, anticipating the catastrophic effect of natural phenomena and the modern concepts of geoethic.